In recent years, photo-fabrication processes for forming three-dimensional objects consisting of integrally laminated cured resin layers prepared by repeating a step of forming a cured resin layer by selectively irradiating a liquid photo-curable material with light have been proposed (see Japanese Patent Application Laid-open No. 247515/1985, U.S. Pat. No. 4,575,330 (Japanese Patent Application Laid-open No. 35966/1987), Japanese Patent Application Laid-open No. 101408/1987, Japanese Patent Application Laid-open No. 24119/1993).
A typical example of such a photo-fabrication process comprises forming a curable resin layer having a specified pattern by selectively irradiating with light using, for example, an ultraviolet radiation laser on the surface of a liquid photo-curable material (photo-curable resin composition) in a container, feeding the photo-curable resin composition equivalent to one layer to form another thin layer of the composition over this cured resin layer, and selectively irradiating this thin layer with light to form a new cured resin layer which is integrally laminated over the previously formed cured resin layer. This step is repeated a number of times, with or without changing the pattern in which the light is irradiated to form a three-dimensional object consisting of integrally laminated multiple cured resin layers. This photo-fabrication process has been attracting considerable attention, because the target three-dimensional object can easily be prepared in a short period of time even if it has a complicated shape.
The following resin compositions (A) to (C) represent photo-curable resin compositions conventionally used in the photo-fabrication process.
(A) Resin compositions containing a radically polymerizable organic compound such as urethane(meth)acrylate, oligoester(meth)acrylate, epoxy(meth)acrylate, thiol-ene compounds, photosensitive polyimide, and the like (see Japanese Patent Applications Laid-open No. 204915/1989, No. 208305/1990, and No. 160013/1991).
(B) Resin compositions containing a cationically polymerizable organic compound such as an epoxy compound, cyclic ether compound, cyclic lactone compound, cyclic acetal compound, cyclic thioether compound, spiro-orthoester compound, vinylether compound, and the like (see Japanese Patent Application Laid-open No. 213304/1989).
(C) Resin compositions containing a radically polymerizable organic compound and a cationically polymerizable organic compound(see Japanese Patent Applications Laid-open No. 28261/1990, No. 75618/1990, and No. 228413/1994).
The characteristics required of the photo-curable resin composition used for these photo-fabrication processes include a low viscosity to quickly form a smooth liquid surface and the capability of being rapidly cured by irradiation with light. Also, the required characteristics of the photo-curable resin composition are minimal swelling of the cured products and minimal deformation due to shrinkage during curing with light, so as to minimize the production of defective parts such as warped parts, indented parts (sinkmark), or stretched parts (overhanging parts).
Three-dimensional objects prepared by photo-fabrication methods have conventionally been used for design models, trial mechanical parts for confirming the functionality, or masters for molds. In order to use this process for trial mechanical parts, it is important that the three-dimensional object has high dimensional accuracy in accordance with the design in fine processing, mechanical strength and heat resistance sufficient to withstand conditions of use.
However, no conventional resin composition can satisfy the above demands. The three-dimensional objects obtained, for example, from the above-mentioned resin composition (A), which is a resin composition containing a radical polymerizable organic compound, such as urethane(meth)acrylate, oligoester(meth)acrylate, or epoxy(meth)acrylate, exhibit problems of deformation with the passage of time, such as production of warped parts, or indented parts, or stretched parts (overhanging parts), because of residual strain due to the shrinkage during curing. These problems of deformation with the passage of time can be partly solved by the correction of the input data to the CAD. However, CAD corrections are insufficient to compensate for modern trial mechanical parts which have intricate and complicated shapes, or for circumstantial variations of use.
The above-mentioned conventional resin composition (B) include a cationically photo-polymerizable compound containing an epoxy compound have drawbacks that the photo-curing rate of the resin solution is lower than that of resin compositions including a radically photo-polymerizable compound in photo-fabrication processes, necessitating the processing time to be prolonged. Also, three-dimensional objects prepared by photo-fabrication using resin compositions including a cationically photo-polymerizable compound containing a conventionally known epoxy compound are not provided with sufficient toughness required for the trial mechanical parts used for confirming the functionality.
Only an insufficient photo-curing rate can be provided using even hybridized photo-curing resin compositions including, for example, (meth)acrylate monomer which is the above-mentioned radically photo-polymerizable compound (C), and an epoxy compound which is a cationically photo-polymerizable compound.
The present invention has been achieved in view of this situation and has an object of providing a photo-curable resin composition used for photo-fabrication, which can be rapidly cured to ensure reduction in the period of time required for photo-fabrication processes. Also, the present invention has an object of providing a photocurable composition used for photo-fabrication, which can provide three-dimensional objects which have high toughness and dimensional accuracy.